Post-traumatic stress disorder (PTSD) might be seen as an occupational hazard from serving in combat, but almost 8 percent of people in the UK have it by the time they turn 18. Yet most are not getting treatment, despite the shockingly high risk of suicide.

Trauma in young people, and the long-term effects on their mental health is a relatively under-researched area. Studies of the frequency of childhood PTSD in the US and Europe used diagnostic criteria now considered out of date. To address this, Professor Andrea Danese of King's College London led interviews with more than 2,000 adolescents born in England and Wales when they were 18.

In The Lancet Psychiatry, Danese reports that 31 percent of those in his sample had experienced a traumatic event in their childhood, such as witnessing deaths or experiencing severe injury or sexual violation. Many of those involved suffered from “network trauma”, where they were affected by something they didn't personally witness that happened to someone they were close to.

PTSD, which can manifest in having nightmares about the event, avoiding things that might remind a person of their trauma, or misplaced guilt, was identified in a quarter of those who had experienced trauma, including three-quarters of those who suffered sexual assault. PTSD frequently has broad life effects by making it harder to study or hold down a job.

Most of those Danese's team diagnosed with PTSD had not received treatment. Just one in five saw a mental health professional, and only a third had discussed their mental health with a GP in the previous year. This was despite three-quarters of those with PTSD having at least one other mental health condition, most commonly a major depressive episode. Almost half had self-harmed and one in five had attempted suicide, 11 times the rate for those who hadn't experienced trauma.

“Childhood trauma is a public health concern yet trauma-related disorders often go unnoticed. Young people with PTSD are falling through the gaps in care and there is a pressing need for better access to mental health services,” Danese said in a statement.

First author Dr Stephanie Lewis noted that the consequences of childhood PTSD become “increasingly difficult to assess and treat” with time.

Participants were all twins, both identical and non-identical, drawn from an ongoing study of twin development. They had been interviewed four times between the ages of five and 12, with questions to them and their parents that were useful for this research. There is no obvious reason to think twins are more likely to suffer PTSD than other children.

With many of the most common causes of trauma being far more common in the United States, the occurrence is likely to be even higher across the Atlantic.